Pretty sure it is 100 % of Maximum Energy on the Vital Fraction Cost. I would use a switch effect, many different validators, and many different possible behaviors/apply behavior effects as well. Validators will basically check how much energy they have at the time, can do checks for 50, 100, etc, 10, 20, etc, however fine tuned you wish to make it. Behaviors will have varying lengths/strengths whatever you decide. And Apply Behavior effects will obviously be applying said effect to the caster. Just be sure to run something at the end to remove all energy too.

A switch effect is a "Set" effect with validators tied to each effect in it (And, by default, only runs one effect). Just create one and take a look, it should be rather straight forward. Make sure to list the effects starting with the highest energy validator, because once one of the effects are fired it will skip the rest (unless told to do otherwise, which you dont want anyway), so if you ordered from smallest to highest it would always pick the lowest.

All it does is toggles a radar like the sensor tower radar or seige tanks range On/Off
I used a switch so that i only needed one button in the command card.
But obviously this ability has a different range because its a fire